Last night I drove my girlfriend home, and I was really low on fuel. I made it all the way there and back, no problem. Right when I turned on my block, it started bucking and running way lean, like off the scale on my AEM Lambda gauge. I thought it was from being low on fuel, no big deal. I filled up the tank and it still is running very, very lean. Accelerating from stop I'm at 1.00-1.10, and cruising its as high as 1.25-off the scale. That's bad.

Things that have changed lately:

1. Earlier that night I changed the o-rings on my injectors. I run E85 and the ethanol destroys the rubber o-rings around the seat of my injectors, so I swapped them out.

2. It's winter and the E85 switched to E70. I don't think that would cause this big a problem.

3. I unbolted the back half of my exhaust. I have a test pipe in place of a catalytic converter, and it has the lambda gauge sensor there. I unbolted everything from after the sensor back.

I have a Walbro fuel pump and SARD FPR. I checked the FPR and at idle it's at a cozy ~45 psi. I don't think the lambda gauge is messed up, because the engine was definitely misfiring from being so lean. One thing I did notice though is that my battery is only showing ~11V at idle. That's not right, is it? If my battery isn't cranking enough volts to the fuel pump, could that cause it to run lean? But if the fuel pump wasn't putting out enough fuel, wouldn't that show by low fuel pressure at the FPR? I'm lost... Please help!

should be charging at more then 12v, any lower then that you start having problems, like your car might not restart. if you have a battery tender, put it on over night and check in the morning to see if your battery held a charge

I tried a different battery, it too only showed 10.5-11v at idle, so it's not my battery. Could it be a crossed wire or bad ground? Something has to be draining the power.

I don't think it's anything with the fuel system. I can hear the fuel pump whine when I turn the key to ON. I just changed the fuel filter this afternoon, and I'm showing 45-50 psi on the FPR at idle. I unplugged each injector one at a time and the idle noticeably dropped, so I believe the injectors are ok.

Other possibilities:

Bad O2 sensor - How do I check that?I have a SAFC piggyback and one of the airflow wires could be disconnected, causing the SAFC to not be working. I run E85 so the SAFC has to be working or else I'll run lean.If the battery isn't putting out enough juice to sufficiently power the pump and injectors, could it cause the car to lean out? What voltage should they see?

If for some reason you pinched one going in or you have a defective o-ring you could be getting air into cylinder. It gets sucked in where the bad o-ring is and casues your motor to run lean, misfire, ect.

I never even thought about that. I just assumed they seated fine and I disregarded that as a potential cause. That would make perfect sense, wouldn't it? Ocham's Razor - the simplest explanation is probably the correct one! I'm working now but I'll try that when I get home. Thanks 14k!

On that subject, anyone know what kind of o-rings I should use, especially when using E85, and where I can get them? I tried crappy ones from pepboys, and apparently they are no good. Thoughts?

I tried a different battery, it too only showed 10.5-11v at idle, so it's not my battery. Could it be a crossed wire or bad ground? Something has to be draining the power.

If the battery isn't putting out enough juice to sufficiently power the pump and injectors, could it cause the car to lean out? What voltage should they see?

I'm out of ideas everyone. I need help! Team effort!

with out your car running the battery should be at 12v or just under that, when running you should be charging at 13-14v, maybe take your alt. into a parts store, have them see if its good or bad. around me all the parts stores do it for free! also check for blown fuses, and maybe clean up your battery terminals.

If for some reason you pinched one going in or you have a defective o-ring you could be getting air into cylinder. It gets sucked in where the bad o-ring is and casues your motor to run lean, misfire, ect.

your low voltage may be a seperate problem.

Try doing your O-rings again

easy way to check if o-rings are bad is to spray brake cleaner or starting fluid around the injectors while its running, and listen to see if there are changes in idle.

No luck. I replaced the injector o-rings and it's still running lean. Sprayed them with silicon lube and seated them right. Still running lean. Although, I sit here wondering if I should have changed all 3 o-rings on each injector... Are the lower o-rings as important as the ones that seat the injectors in the fuel rail? I've never changed those lower ones...

But I also tried spraying down the intake gasket, IACV gasket, throttle body gasket, injectors, and vacuum lines with carb and choke cleaner and I never heard any idle change...

I didn't check the bottom o-rings yet, that's next. I think I'll do a boost leak test too, just for peace of mind. I'm also gonna pull my fuel pump and visually inspect it to make sure it looks undamaged. I'll update later today after I try these things. Thanks so far for all the suggestions.

The battery is still not charging right, and I found that problem. The main power cord coming out of the alternator was totally corroded and about half of it was broken off at the terminal. I wiggled it only the slightest and it totally snapped. So now that problem is found, does anyone think that could have caused the car to lean out? I'm not convinced this did it... Sure, it was a definite problem, and that will charge my battery better, but I don't think this would screw things up enough to cause my car to run lean.

I've decided to do this diagnosis straightforward:

The car needs fuel, air, and spark to run.

I'm convinced it's not a fuel leak. Fuel pump turns on, brand new filter, no leaking injectors or o-rings, FPR shows ~50 psi at idle and holds at ~40 psi after I turn the key off. I even pulled the fuel rail with the injectors still in, and the lower o-rings don't leak either. It held perfect pressure. I also pulled the injector connectors one at a time and each time the idle dropped noticeably. So unless anyone has any objections, I'm closing the fuel system as ok.

Spark doesn't really make sense. If there was a problem, it would most likely have a lack of spark, not excess spark, causing the car to run rich not lean. It has brand new plugs. I also just checked my timing, base is 16* which is just fine. So, again, if anyone has any other ideas I'm saying spark is fine.

This leaves air. Could a boost or vacuum leak cause unmetered air to enter the system causing lean conditions? Or a leaking intake manifold gasket? I was under the impression that if it was an air leak, at idle there is a vacuum so unmetered air would be pulled into the intake system causing leanness, but under even the slightest boost the system is in positive pressure, so air would be leaking out not in, making the car run rich. But this is not the case; the car is lean all the time.

So that's my thought process so far. Any more ideas? Is any of my thinking incorrect? Any advice would be greatly appreciated. Thanks in advance everyone.

It was the bad alternator cable. I cleaned up the corrosion, put a new terminal on it, new nut and hooked up the battery. 14.5v steady. Started the car, let it idle for 5 minutes, no leaning out. Went out for a spin, perfect. Battery was holding 14-14.5v, A/F ratios were perfect, it's absolutely fine now. Woo! I can't believe that was it... Oh well, stranger things have happened. Thanks for all the suggestions everyone. I'm really glad it's solved!

Not strange at all, pumps are very sensitive to voltage input vs. flow. If you haven't already you really should add a relay to the pump circuit and use the factory pump wire to turn the relay on. That gave me better pump performance in my car.